#ifdef DEBUG versus #if DEBUG

Question

It is unclear to me when using compiler directives which of the below two code snippets is correct/preferred and why. It seems that most developers and Open Source projects I\'v

Answer 1

As I know, the finest choice is:

#ifndef DEBUG
    NSLog(@"-1");
#elif DEBUG == 0
    NSLog(@"0");
#else
    NSLog(@"%d", DEBUG);
#endif

then, you will know #ifndef DEBUG is preferred above all others.

There is a simpler choice:

#if DEBUG == 0 // DEBUG is not defined or defined to be 0
    // do sth
#else
    // do sth
#endif

However, if -Wundef compiler flag is on, there might be a warning with #if DEBUG == 0.